What should my manifold vacuum be?

[leostevo]

I have the 360 with a Edelbrock Performer Package installed on my motor, to include the carb, intake, exhaust and cam.

I just bought a vacuum gauge and hooked it up to my manifold. It bounced around between 5 and 15. When I revved the motor it moved appropriately but still bounced significantly.

I know that a huge cam will cause lots of bouncing but is the edelbrock performer cut "huge?"

I disconnected/plugged the vacuum bulb at the end of the motor and used the brake hose to hook up my gauge.

I know there is something you can spray around the carb and intake to check for leaks, is it ether/starting fluid? I also adjusted the carb using the guage as my guide and couldn't raise the vacuum any more. I don't have a timing light but I think it was set to about 12' when I installed the motor.

[Jeepguy77]

you can spray water, carb cleaner, brake cleaner etc. while spraying listen for the engine to smooth out and the revs to go up a little.

[leostevo]

I'll try that tomorrow. God I hope the intake is not leaking. . .

Can anyone tell me what I should expect for the idle vacuum? I realize it shouldn't be shaking but how much higher should I expect the vacuum to get with my setup?

[Jeepguy77]

I cant give you a base line for vacuum, since theres a lot of things to consider such as altitude, engine age, etc. you just want to have the highest vacuum reading you can get and a rock steady needle on the gauge.

[ag98gie]

vacuum: http://www.ifsja.org/tech/motors/vacuum.html

timing: http://www.ifsja.org/tech/motors/85timing.html

[ag98gie]

At the bottom of the page you are currently viewing is a listing of "similar threads", this is one of them:

http://www.ifsja.org/forums/vb/showthread.php?t=48971

[leostevo]

Well, I suppose I could have mentioned that the motor has less than 1000 miles on it and that I am on the coast (about 32ft above sea level).

I understand how to tune it. I was looking for what the maximum vacuum generally is with the edelbrock performer cam. I know that BIG cams will reduce the vacuum and cause needle shake but how BIG does it need to be to be considered such?

I messed with the timing some and got the vacuum up to 16" and I also learned this little tidbit:

A vacuum pump does not have a dampner in it. A vacuum gauge does. Put a small orifice inline before the vacuum pump and you have a dampner.

Now my needle shakes about 1" each way from center. . . Acceptable? Should I still be looking for a leak? I sprayed carb cleaner all around the intake and carb after plugging off all vacuum hoses; no change in engine speed.

So, I suppose the question now is this: Am I looking for a problem where there isn't one?

[mattmopar440]

Be very careful with that Brake Clean or Carb clean Method !!!!!!!!

Get that stuff close to your Exhaust system and you'll have more then a Vacuum leak Problem Trust me

[leostevo]

Oh I was very specific about exactly where that stuff went. I thought about the whole fire in the engine compartment thing, but the real care was from not knowing what kind of chemicals might screw up the finish on all my chrome.